Various types of downhole tools are conveyed into a wellbore on a wireline or similar cable for operation once a predetermined depth or position of the tool in the wellbore is reached. Since such tools must often be lowered through several thousand feet of wellbore, it is desirable to have a positive indication of when the tool has been actuated so that the intended operation of the tool may be carried out. Moreover, if the tool is inadvertently actuated prematurely, positive indication of this event is desirable to minimize time in retrieving the tool for correction of the fault.
One type of tool which is adapted for mechanical actuation upon reaching a predetermined depth is a wellbore fluid sampling apparatus. Various types of wellbore fluid sampling devices are known which are actuated upon reaching a predetermined position in the wellbore to trap a fluid sample in a closable chamber so that the sample may be retrieved for analysis at the surface. In this regard, there has been a need for a mechanically uncomplicated and reliable device which will give a positive indication at the surface that certain events have taken place in connection with operation of the sampler or similar downhole tools in order to confirm that the intended operation of the tool has been carried out or to alert the tool operator to the fact that a premature or unwanted actuation of the tool has occurred so that retrieval of the tool can be effected with minimum loss of time and effort. The present invention provides such an improved and unique device as will be appreciated by those skilled in the art upon reading the further description set forth herein.